Lighting of buildings and outdoor areas is a large part of global electricity consumption. At least in part because of this, the use of energy inefficient lighting, including fluorescent lighting, induction lighting, incandescent lighting, is typically being phased out through promotion of more efficient lighting systems.
In conventional fluorescent lighting, electric current in the gas phase excites mercury or other ion vapor which produces a broad range of ultraviolet (UV) light, in addition to visible light. The UV light in turn causes a phosphor coating on the inside of the bulb to glow. Combination of converted and directly emitted visible light makes up the total output. Conventional fluorescent lighting systems may use multiple phosphors that coat the inside wall of a fluorescent tube. However, much of the UV radiation created by the discharge is not used because it is not absorbed by the phosphors, and is filtered or reflected back into the tube, which makes the devices less efficient and/or more costly to manufacture.
Conventional induction lighting operates in a similar way to fluorescent lighting, but without the need for electrodes. The excitation of the ions in the gas phase is done externally by electric or magnetic field. Induction lighting typically emits the same broad spectrum as a fluorescent lamp, but may have a longer lifetime and higher durability. However, due to multiple phosphors and a mixture of directly emitted visible light and converted UV light, the color rendering index is typically poor.
Conventional fluorescent or induction lighting that uses phosphors may only convert a narrow range of wavelengths into visible light. As well, multiple phosphors emitting complementary colors are generally needed to approximate white light. Further, conventional phosphor-based lighting typically uses expensive rare earth elements.
As such, there is a need for new high-efficiency lighting sources to reduce electricity usage. Solid state lighting, and in particular light emitting diodes (LEDs), have emerged as a promising long-term solution that could meet stringent efficiency, safety, durability, and reliability standards. Currently, LEDs are found in a wide variety of applications, including general lighting, automotive industry, architectural lighting and displays. White Light Emitting Diodes (WLEDs) are traditionally based on a multicolor (RGB) approach, in which white light is generated by controlled mixing of the emission from blue, green, and red LED chips. More recently, WLEDs have primarily been fabricated by combining a GaN blue LED chip with one or more phosphors, most notably yellow-emitting yttrium aluminum garnet doped with cerium (Ce3+:YAG). These GaN/Ce3+:YAG and similar phosphor-converted WLEDs generally suffer from a deficiency in the red emission component, resulting in low color rendering index (CRI <80%) and high correlated color temperature (CCT ˜7000 K). The past decade has seen an ongoing effort to develop rare earth element-based converters that could produce optimal quality white light in conjunction with blue LEDs. However, increasing deficiency and strategic importance of rare earth elements call for investigating other approaches to WLEDs. The slow adoption of WLED technologies is exacerbated by complex design and inconsistency of key figures of merit, ultimately leading to high device manufacturing cost.
While LEDs and WLEDs in particular are being used in some applications, there remain other applications where LEDs may not be as effective, for example, larger area lighting such as that for larger buildings (e.g. warehouses, open-floor office spaces and the like) and outdoor lighting (e.g. parking areas, stadiums, and the like). In these applications, it is likely that fluorescent lighting, induction lighting or halogen lighting will be used. As noted above, conventional fluorescent and halogen lighting systems also have some drawbacks, including the use of rare earth metals in the phosphors and mercury vapor in the gas phase to provide the light output. These materials can be expensive and/or dangerous. Further, conventional lighting approaches may require electrical ballasts to regulate the current passed through the lamp. Ballasts generally make the lighting bulky and costly. Conventional lighting approaches may also generate UV light which can have harmful effects if not converted or blocked.
There is therefore a need to provide a new lighting material, a method of producing the same, and fluorescent lighting systems making use of the new lighting material that can generate a desired quality of white light in an energy-efficient and economically viable way.